Ceàrn dùbailte
Bhon triantan gu h-ìosal tha \(\tan x = \frac{{\sqrt {13} }}{6}\). Obraich a-mach an luach mionaideach aig \(\cos 2x\).
Cleachd Teoram Phythagoras agus obraich a-mach a' hypotenuse, a' toirt dhut \(\sin x = \frac{{\sqrt {13} }}{7}\) agus \(\cos x = \frac{6}{7}\).
Faodaidh tu foirmle sam bith de na trì a chleachdadh airson \(\cos 2x\).
A' cleachdadh \(\cos 2x = {\cos ^2}x - {\sin ^2}x\)
\(= {\left( {\frac{6}{7}} \right)^2} - {\left( {\frac{{\sqrt {13} }}{7}} \right)^2}\)
\(= \frac{{36}}{{49}} - \frac{{13}}{{49}}\)
\(= \frac{{23}}{{49}}\)
